I'm a Theravadin, but I'd like some help finding some Mahayana-oriented resources.

There are a lot of extensive talks by Theravadin monks and scholars on Youtube and other websites, so as a Theravadin I have very easy access to various interpretations and explanations of Buddhist thought and practice from within my own tradition.

My question is, have Mahayana monastics made material like this similarly available and freely accessible? Are there prominent monks and nuns (other than the Dalai Lama and Thich Nhat Hanh) who lecture widely and extensively on the dhamma?

berzin archives should have some recorded talks, if not then at least a lot of material in text format.

Robina Courtin is a gelugpa and student of Lama Yeshe and Lama Zopa Rinpoche, she has some amount of talks on youtube on different Mahayana subject and little bit of vajrayana. you can find for your likings when you search her name on youtube.

Lama Zopa Rinpoche should have some Dharma talks, remember if you listen to dedicate to his long life

If the thought of demons Never rises in your mind, You need not fear the demon hosts around you. It is most important to tame your mind within....

In so far as the Ultimate, or the true nature of being is concerned, there are neither buddhas or demons. He who frees himself from fear and hope, evil and virtue, will realize the insubstantial and groundless nature of confusion. Samsara will then appear as the mahamudra itself….

archive.org has numerous Dharma Talks available for download. Many are from the Tse Chen Ling center, which I believe is part of fpmt.org. There is also a guy named Tamarack Garlow that has some short (30mins) talks/commentaries about different aspects of Buddhism, I believe he is Tendai though. The archive has more stuff than you probably have time to listen to.

May you have happiness and its causes,May you be free from suffering and its causes

May you always find happiness and its causesMay you always be free from suffering and its causes

In the Tibetan tradition there are countless talks on youtube by highly regarded teaches such as HH Dalai Lama, the Karmapa, Lama Zopa Rinpoche, Dzongsar Kyentse Rinpoche etc. - there is no shortage.

In terms of the non-Tibetan Mahayana traditions,Ven. Heng Sure is an American monk ordained over 20 years in the Chinese Buddhist tradition of Master Hsuan Hua. His lectures on the Avatamsaka Sutra as especially interesting:

In order to ensure my mind never comes under the power of the self-cherishing attitude,I must obtain control over my own mind. Therefore, amongst all empowerments, the empowerment that gives me control over my mind is the best,and I have received the most profound empowerment with this teaching.-Atisha Dipamkarabrtsal ba'i bkhra drin